Do you want to learn how to use dnl in Sendmail? Our Server Management Support team is here to lend a hand with your queries and issues.

An Introduction to dnl in Sendmail

Did you know that the m4 macro processor is responsible for processing the sendmail.mc file to generate sendmail.cf file?

The sendmail.mc file includes macros that portray our preferred configuration. These macros are expanded by the m4 macro processor.

The dnl command is used in the sendmail.mc file. This command signifies ”delete through newline”. When the m4 macro processor comes across the dnl line in the configuration file, it drops everything after the command, including the next new line.

In other words, any lines in the configuration file with dnl at the beginning will not make their way into the sendmail.cf file.

However, if we want a particular line to remain in the sendmail.cf, we can add # at the beginning of the line rather than the dnl command. A line with # at the beginning will appear as a comment in the cf file.

In other words, we can use the dnl command to signify lines that we do not want to wind up in the configure script file. The dnl command prevents m4 from parsing that line.

So if you do not want a particular line to appear in the sendmail.cf file after passing it through the m4 processor, the dnl command is your answer. Let us know in the comments if this article helped you understand how the dnl command works.

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Conclusion

To wrap up, our Support Engineers introduced us to the dnl command in Sendmail.